This invention relates to measurement of carrier mobility and density in semiconductor materials and more particularly to contactless measurements without any deleterious effects on the material.
It is well-known in the art that many semiconductor devices are made of different materials and with different thickness of layers which may be as thin as 25-50 Angstrons with current molecular-beam epitaxial technology. Such thin structures make it very difficult to measure different electrical characteristics. Thin layers are not conducive to connecting electrical contacts thereto because of the probability of damage to and for modification of the surface.
Heretofore measurements have been made by electrically contacting the layer in a semiconductor and making Hall and resistivity measurements. Analysis of the obtained data yields the electron concentration and the Hall mobility. Making ohmic contact is difficult, time-consuming, and destructive since a portion of the layer to be measured must be modified in making the contact. Making measurements of ion-implanted layers is particularly difficult, since annealing of induced damage must be carried out. For compound semiconductors, the sample must be encapsulated prior to the annealing state in order to prevent vaporization of any of the constituents. In this case, conventional Hall and resistivity measurements cannot be carried out unless the encapsulant has been stripped off. This requires additional time and effort and makes any study of annealing behavior extremely difficult and time-consuming.
This invention overcomes the disadvantages of the prior methods because the measurement is contact-free and requires no connections or modifications to the semiconductor structure during measurement.